Irrigation and Nitrogen Effects on Tall Wheatgrass Yield in the Southern High Plains

Winter months in the Southern High Plains of the USA have the lowest precipitation. As a result, producers using tall wheatgrass [ Agropyron elongatum (Host) Beauv.] may get higher production in the spring and possibly throughout the growing season with additional irrigation. Also, growers need information about interactions between soil moisture and N fertilizer to maximize productivity. In a split‐plot study conducted at the New Mexico State University Agricultural Science Center at Tucumcari from 1997 to 1999, tall wheatgrass furrow‐irrigated monthly from April to September was irrigated once, twice, or not irrigated during winter as the whole‐plot treatment. For subplot treatments, tall wheatgrass annually received 168 kg N ha −1 split into two, three, or four equal applications. Tall wheatgrass irrigated in the winter yielded more dry matter (DM) over the 3 yr than unirrigated tall wheatgrass (11.72, 12.10, and 13.55 Mg ha −1 for tall wheatgrass not irrigated, irrigated once, or irrigated twice, respectively). Tall wheatgrass fertilized three or four times outyielded tall wheatgrass fertilized twice (11.08, 12.85, and 13.44 Mg ha −1 for two, three, and four N applications, respectively). No interaction occurred between the irrigation and N treatments. A year × harvest × N effect existed in which a mid‐December N application, preceded and followed by precipitation, produced approximately 1 Mg ha −1 more DM than unfertilized tall wheatgrass in the first harvest the following year. Both supplemental winter irrigation and N application scheduling offer opportunities for tall wheatgrass producers to increase production in the Southern High Plains of the USA.